On LMDE Firefox seems to use a lot of CPU. Htop shows 80+ and even when idle over 50. Way too hot, I believe. Very few extensions, only Adblocker, Lastpass, Xmarks and Mint search. The same configuration on Maya LTS is 5-7% much better behaved. How can I tame Firefox on LMDE?

Firefox uses many low priority threads. A CPU idle, is not an indication of how much work the CPU is doing. Its how much time is waisted by not doing anything. Lets make an example of extremes, the CPU wants to add two pieces of data from the HD. If programmed in a single thread, the CPU is marked active for 15 million processor cycles while it waits for the data to traval from HD to CPU Registers. This is the design of most programs. Firefox on the other hand, (not a firefox expert), might place a queue list of files to get, and constantly checks (polling) using a separate thread if those files have been retrieved into RAM. In most cases, using the second thread, we did much more computation as a whole; but yet do to the design, the processor is more availbale and responseive for any other processor activity. (Its like saying you are using a phone when you are waiting for a call, but not using the phone.)

That or you have some flash running on the webpage. In that case, Flash programming which takes over your processor and doesn't play well with others, until its processor time is over.

Just some insite, perhaps you have something wrong. But also note that percent of time the computer has no instruction to process is different than how hard its working.

Appreciate the insight. Didn't know some of those things. As you can see from the original post, I multi-boot and run Mint 13 LTS, and LMDE as two of those boots. FF is install in each and it much better behaved in Mint 13 LTS taking less CPU resourses. The configuration of FF in both is the same as far as I can tell. So I'm wondering why the CPU demand is so much higher in LMDE. Doesn't make sense to me. btw after further testing the CPU demand in LMDE does drop quite a bit after it has been running a while, but still over double that in Mint LTS.

The newest version of FireFox, 23, is a disaster for me, on Mate 13 64 bit.It lags, it freezes, CPU usage is always high.Measured on a set of everyday usage sites.Version 22 was excellent. Again, same old story, goin' in circles... I think next time I'm satisfied with the performance, I'll pass through the upcoming version.